Pigments such as titanium dioxide are a common component of coating compositions, particularly paint. Paint generally comprises a film-forming material or binder, a pigment, and a carrier or solvent which evaporates to leave the solids as a coating on a substrate.
The pigment is generally partially or wholly suspended or dissolved in the carrier. Film formation of paint occurs when the paint is applied to a substrate and the carrier evaporates. During this process, the particles of pigment and binder come closer together. As the last vestiges of liquid evaporate, capillary action draws the binder particles together with great force, causing them to fuse and bind the pigment into a continuous film. This process is often referred to as coalescence.
Thus, the spacing and orientation in the carrier of the pigment particles relative to each other, and the various other solids, is essentially retained when the solid film is formed on the substrate. Flocculation and settling of the pigment phase are particularly undesirable. The pigments tend to cling together as packed pigment particles by agglomerating or clustering and then tend to resist subsequent redispersion by agitation, thus degrading the hiding power of the resulting paint. Hiding power is among one of the most important attributes of paint, and hiding power is determined particularly in white paint by the light scattering effectiveness of the pigment. The light scattering effectiveness of the pigment is in turn highly dependent on the spacing arrangement of the pigment in the dried coating as well as the particle sizes. Many different methods are known in the art for affecting and controlling the sizes of the pigment particles; however, this has proven to be ineffective in controlling light scattering sufficiently.
The pigment which is most widely used in paint is titanium dioxide. However, titanium dioxide is relatively expensive in comparison to the costs of other components used in paint. As such, there is a need to maximize the beneficial aspects of titanium dioxide, while minimizing the amount used. Enhanced light scattering occurs when the titanium dioxide pigment particles have a diameter of about 200 to 300 nm and are uniformly spaced about the same distance apart. Most commonly, particulate TiO2 in the range of 100 nm to 400 nm is utilized in conventional paint.
Various techniques have been attempted and used in the art to promote an even spacing and distribution of the pigment in the coating. A number of pigments have been found to function as “extender” pigments, wherein the extended pigments are alleged to function in mechanically spacing the opacifying or “prime” pigments. However, the flocculation forces present during the drying of paint still result in the presence of clusters and flocs of pigment particles. Thus, even if total deaggregation is accomplished in the dispersion process, a random distribution of pigment particles will not approach the theoretical optimum that an ideally spaced distribution would achieve.
Regardless of the technique, prior art coatings do not achieve a level of opacity which approaches that predicted theoretically. Thus, there is a long felt need for further improvement, such as a more efficient packing arrangement of TiO2 particles in a coating formed on a substrate.